1. Field of the Invention
This invention relates generally to delay circuits and, more specifically, to a time delay circuit which is voltage independent thereby allowing the time delay circuit to generate a more constant time delay.
2. Description of the Prior Art
Currently, most time delays on integrated circuits are implemented with a Resistor-Capacitor (RC) time constant circuit. The RC time constant circuits may further be used for clocking a counter to create longer delays. The major problem with RC based time delay circuits is that the delay varies significantly with the supply voltage V.sub.dd. As the supply voltage V.sub.dd fluctuates, the RC based time delay circuit will trip at different voltage levels thereby causing the circuit to generate different delay times. Thus, in the prior art Resistor-Capacitor (RC) time delay circuits, the voltage across the resistor changes as the capacitor is being charged. This reduces the charging current thereby charging the capacitor in a non-linear manner.
Therefore, a need existed to provide an improved time delay circuit. The improved time delay circuit will be voltage independent. The improved time delay circuit will be voltage independent thereby allowing the improved time delay circuit to have a more constant trip point and thus generate a more constant time delay.